1. Field of the Invention
The present invention relates to a dispensing device for dispensing powder, in particular, containing or consisting of a drug, as a spray including fine powder particles, and to a storage device for such powders which has at least one, and preferably, multiple separate storage chambers, each containing a single dose of the powder to be dispensed by gas pressure. The invention also relates to a method for dispensing a spray including fine powder particles by means of gas pressure.
2. Description of Related Art
Powder drugs delivered through dispensing devices, in particular, inhalers, are intended to optimally target specific sites in the pulmonary system. These sites include the nasal passages, the throat, and various locations within the lungs, such as the bronchi, bronchioles and alveolar regions. The ability to deliver drugs to a target area depends, inter alia, on the aerodynamic sizes of the particles. As currently believed to be understood, particles having an aerodynamic diameter of less than 2 μm are considered to be potentially optimal for deposition in the alveolar region of the lung. Particles that have an aerodynamic diameter of between 2 and approximately 5 μm may be more suitable for delivery to the bronchiole or bronchi regions. Particles with an aerodynamic size range greater than 6 μm, and more preferably, 10 μm, are typically suitable for delivery to the laryngeal region, throat or nasal passages.
In most cases, it is desired to achieve a high inhalable fraction and a high delivery efficiency, i.e., the fraction that reaches the desired region, in particular, in the lung. This depends on various factors, in particular, on the characteristics of the generated spray plume, such as propagation velocity of the plume, particle size and its distribution, fraction of small particles, fraction of gas and the like. In the present invention, the desired spray plume characteristics include preferably, a small particle size, a high fraction of drug particles with a diameter of 6 μm or less, a low propagation velocity, a long duration of spray generation and/or possible inhalation, and/or a low amount of gas volume required for dispensing a certain amount of powder.
In particular, the present invention is concerned with dry powder inhalers for the delivery of drugs to the lungs. Many dry powder inhalers are on the market or have been proposed. There are two main types, namely the passive ones and the active ones. In passive inhalers, all the energy required for de-agglomerating the powder and transferring the powder to the lungs is provided by the breathing of a user or patient. In active inhalers, there is an additional source of energy to help to de-agglomerate the powder.
Most powder inhalers are of the passive type where the powder is inhaled by the patient without the aid of an additional energy source. The problem with passive inhalers is that the inhalable fraction, or the proportion of powder that actually enters the lungs, is largely dependant on the breathing of the patient. The de-agglomeration of the powder and hence the inhalable fraction is a function of the flow rate of inhaled air through the device and, therefore, varies greatly from patient to patient.
Dry powder inhalers are subdivided into single dose devices and multi-dose inhalers. Multi-dose inhalers are further subdivided into pre-metered types where the doses are stored individually and into metering inhalers where the powder dose is metered in the device.
Multi-dose pre-metered inhalers have the advantage that the single doses are metered under strict factory conditions and the powder can quite easily be isolated from the atmosphere. In many applications, the active duct powder is mixed with a carrier, such as lactose which tends to absorb humidity from the atmosphere which makes it stick together and difficult to de-agglomerate.
The present invention relates, in particular, to an active, gas powered, pre-metered multi- or single-dose dispensing device for dispensing powder containing or consisting of a drug, such as a dry powder inhaler.
International Patent Application Publication WO 92/12799 A1, which forms the starting point of the present invention, discloses a pre-metered dispensing device for transforming a flow of fluid into a spray of fine particle size, wherein an annular flow through a duct is caused with a velocity gradient within that flow sufficient to cause sheer forces between components of the flow to break the flow up into a spray. The cross-sectional shape of the duct is preferably, circular, but other cross-sectional shapes, for example, an irregular cross section or a polygonal cross section can be used. However, the known device and method are not optimal for de-agglomerating the powder and for generating a slow spray plume with the desired characteristics.
International Patent Application Publication WO 2004/041326 A2 disclose a tubular nozzle for use in systems for delivering medicaments, in particular, for metering devices for dispensing liquid aerosols, i.e., so-called metered dose inhalers (MDIs). The tubular nozzle is curvilinear throughout a defined length and has a curved portion with a radius of curvature of at least 2.5 times the inner diameter of the tubular nozzle. The cross section of the tubular nozzle may be selected from a wide range of choices such as circular, oval, square, rectangular, polygonal, and the like.